If you have an old one piece heat pump that sits outside your house and is tasked with keeping your house cool in the summer, it could probably benefit from additional insulation.
1 roll heavy duty aluminum foil.
scrap foam or Styrofoam
Step 1: position and tape down your foam on to the heatpump.
I insulated the section that felt cool to the touch when running, cause it meant that I was cooling something that was being heated by the sun.
most old heat-pumps are in the shape of a box with a round fan molded to the end of it. We are going to insulate the box part.
tape your foam to the surfaces that feel cool to the touch, or if you have had the panels off, put your foam on the surfaces that cover the air handler.
I deconstructed an old foam drink cooler for my insulation panels.anything from 1-3" thick will work.